Re: Coal Bearing Depositional Systems Pdf Download
Gabelo Clancy
Includes two plates. Plate 1: Genetic-stratigraphic cross section of the coal-bearing Williams Fork Formation, Piceance and Sand Wash Basins, Colorado. Plate 2: Cross section indicating missing and duplicated strata due to faulting (9S-91W through 9S-89W) Piceance Basin Colorado. Uses genetic stratigraphy to correlate Williams Fork coal zones between Sand Wash and Piceance Basins. Cross sections delineate major depositional systems and show rationale for coalbed methane target generation and resource estimates. 2 plates. Digital PDF download. OF-97-07D
1990s, basin, CBM, coal, DOI, download, energy, free, Garfield, geophysics, Mesa, Mesaverde, methane, minerals, Moffat, OF-, pdf, Piceance, Piceance Basin, publication, resources, Rio Blanco, Sand Wash Basin, stratigraphy, Western Slope, Williams Fork, x-section
The Rio Bonito Formation (Paraná Basin) contains the thickest coal beds in Brazil, that are related to peat-swamp developed in coastal depositional systems during the early Permian. This study aims to understand the source of the coal organic matter and to distinguish depositional sub-environments along the coal-bearing interval from the southern border of the basin. The analysis was performed on sedimentological and stratigraphic data from 10 wells combined with organic petrology and geochemistry of the three coal beds. Samples were collected in different key beds from the SG-14 well, in different and strategic depths at the base (218.0 m), at the intermediate (209.0 m), and at the top (181.0 m) of the coal-bearing interval. The vitrinite reflectance measurements of the selected samples, Tmax values, C29 ααα 20 S/(20 S + 20 R) ratio, and the absence of peak Ts (and presence of peak Tm) revealed the organic matter in the coal-bearing interval is thermally immature, suggesting low burial depth for the Rio Bonito Formation in the study region. Maceral composition showed predominance of vitrinite and inertinite in the three coal samples. Rock-Eval pyrolysis data indicate that the coal beds are composed of type III kerogen in the three samples, while the biomarkers indicate type II-III kerogen mixtures. The n-alkane distribution profiles suggest dominance of terrestrial organic matter in the samples, with a possible marine contribution at the top of the coal-bearing interval. The pristane/phytane (Pr/Ph) and C27/C29 ααα20 R ratios (regular steranes) revealed sub-anoxic condition and land plants as major organic matter source for basal and intermediate parts of the coal-bearing interval. They also indicate an increased anoxic conditions and possible marine algal contribution toward the uppermost coal level. The presence of cone-in-cone-shaped structures (SG-07 well, depth 157.5 m) and Orbiculoidea fossils (SG-14 well, depth 192.5 m) are indicative of brackish water and support river-marine source mixtures at the top of the coal-bearing interval. The evolutive sedimentation model comprises four paleoenvironments for the Rio Bonito Formation along geological time, in which the basal part of the coal interval is interpreted as overbank deposits in a fluvial depositional system. On the other hand, the intermediate part of the coal-bearing interval was formed in bay-head delta, and the upper part was deposited in the central estuary, both in a tide- and wave-influenced estuarine context.
The late Palaeozoic coal-bearing Madzaringwe Formation of the Karoo Supergroup in the Tshipise-Pafuri Basin in the Limpopo Province, South Africa, records part of the infill of a passive continental margin terrain. Lithofacies analysis was performed with a view to deduce the nature of depositional environments of the Formation. Sedimentological and sequence stratigraphic evidence indicates that this unit represents a complex siliciclastic facies that reflects a fluvial paleodepositional environment. Eleven facies, which were grouped into five facies associations, were recognised. The base of the Madzaringwe Formation (Lower Member) represents a sequence deposited by braided channels. The coal deposits represent flood plain and swamp deposits, which is characterised by shale, thick coal seams, siltstone, and sandstone. The Middle Member is characterised by both clast and matrix supported conglomerates, major tubular and lenticular sandstones, and finely calcareous, micaceous siltstone. The deposition represents a sequence being formed from fluvial and particularly braided channels. The crudely stratified, coarse to pebbly sandstone indicates channel lag deposits within a heavy loaded fluvial system. The fine-grained sandstone represents deposition by shift channel and side bar deposits during lower flow conditions. The Upper Member is characterised by facies associations similar to the Lower Member, representing a new depositional cyclothem.
The sedimentology of the Madzaringwe Formation was analysed in detail at a number of localities among the Tshipise-Pafuri Basin (Figure 1). Detailed review of the spatial stratigraphic variation of the successions, including the analysis of facies changes based on over 500 widely distributed borehole records, field observations, and paleocurrent measurements was performed. The above mentioned set of borehole data resulted from the extensive coal exploration activities in the study area by different companies over the past 50 years. Many units were walked out in order to characterise their regional extent and architecture. Detailed facies and architectural analyses were performed, with particular attention devoted to channel morphology and vertical stacking patterns. Characterisation of bedding hierarchy was carried out by using the classification scheme of Miall [5]. Paleocurrents were derived from planer and trough cross-beddings and asymmetric ripple cross-laminations.
Parallel laminated shale suggests that the sediments were deposited in floodplain environments with frequent variation of energy condition, thus resulting in grain-size variation vertically or laterally. Thin mudstone at top of the channel sandstones indicates deposition from suspension during channel abandonment. The thick dark mudstone associated with coal suggests deposition by vertical accretion in backswamp or flood basin environments [11, 13]. Bands of sandstone and siltstone within the facies association were introduced during periodic events of floods. The presence of carbonaceous mudstone indicates a moderate growth of vegetation in and around the basin.
The thick coal seam indicates a long persistent, slowly subsiding, moderately drained, and densely vegetated backswamp [14]. The thin coal seams contain abundant splits of carbonaceous mudstone that indicates a short-lived flooding during that period. The thick coal seams are thought to result from the combined interaction of various factors, like localised aggradation of channels, slow and steady subsidence of the basin area, abundant rainfall to grow luxuriant vegetation, abundant supply of paleoflora, comparatively higher water table, and long period of stable time [13].
Three identified informal members (lower, middle, and upper) of the Madzaringwe Formation are recognisable. They resemble characteristics of various fluvial depositional environments. The laminated, grey and black carbonaceous shale and coal of FA 5 (Fc, C) and sandy shale/mudstone of FA 4 (F1, Sh, St, and C) form the Lower Member which rests on pre-Karoo rocks or Tshidzi Formation. They display laminated, pyritic, micaceous, and sometimes ferruginous characteristics of a quiet, low energy setting, dominated by slow suspension settling. Coal and carbonaceous shale (FA 5) were probably deposited in well drained swamps whereas peat in poorly drained swamps. Parallel laminated shale (FA 4) suggests that the sediments were deposited in floodplain environments with frequent variation of current energy condition. Thin mudstone at the top of the channel sandstones indicates deposition from suspension during channel abandonment. The thick dark mudstone associated with coal seams suggests deposition by vertical accretion in backswamp or flood basin environments.
The Middle Member is characterised by alternating beds of shale and fine-coarse grained sandstone to siltstone (FA 1, FA 2, and FA 3). FA 1 (Gcm, Se, and St) environments display dominant fluvial braided channels and crevasse splays. FA 2 (St, Sr, and Sh) depositional environments are associated with dominant fluvial channels, crevasse splays, levees and crevasse channels. FA 3 (F1, Sr, and St) depositional environments are associated with shallow lakes in a flood plain setting.
The Upper Member is characterised by facies similar to the Lower Member, laminated, grey and black carbonaceous shale and coal of FA 5 (Fc, C) and sandy shale/mudstone of FA 4 (F1, Sh, St, and C). The coal seams and carbonaceous shale (FA 5) were deposited in swamps. The sandy shale/mudstone (FA 4) was probably deposited in floodplain ponds, lakes, and weakly developed paleosols.
Detailed analysis of lithofacies types and facies assemblages in the Madzaringwe Formation suggests fluvial paleochannel depositional environments. The facies associations identified in the formation resemble those of a fluvial depositional environments dominated by streams, lakes, swamps, and ponds. Three identified informal members (Lower, Middle, and Upper) of the Madzaringwe Formation resemble characteristics of the Facies associations (FA 1, 2, 3, 4, and 5) in a prograding fluvial depositional environment. The laminated, grey and black carbonaceous shale and coal of FA 5 (Fc, C) and sandy shale/mudstone of FA 4 (F1, Sh, St, and C) form the Lower Member of the sequence. The Middle Member is characterised by alternating beds of shale and fine-coarse grained sandstone to siltstone, FA 1 (Se and St), FA 2 (St, Sr, and Sh), and FA 3 (F1, Sr, and St). Succeeding the Middle Member is the Upper Member which has almost the same depositional environments as those of the Lower Member. It is characterised by grey and black carbonaceous shale and coal of FA 5 (Fc, C) and sandy shale/mudstone of FA 4 (F1, Sh, St, and C).
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